any encircling or beltlike structure, either external or internal, longitudinal or transverse

SEE ALSO: area, band, region, space, spot, aka zona.

abdominal zones: abdominal regions, under region.

anal transitional zone: region of anal canal in which the epithelium changes from the simple columnar epithelium of a mucosa to the stratified squamous epithelium of the anoderm (skin); this region is susceptible to a variety of carcinomas. SYN: zona transitionalis analis

androgenic zone:

X zone

fetal reticularis: fetal adrenal cortex. [Named in the belief (as yet unsubstantiated) that the cells within this zone secrete androgens.]

arcuate zone: the inner third of the basilar membrane of the cochlear duct extending from the tympanic lip of the osseous spiral lamina to the outer pillar cell of the spiral organ (of Corti). SYN: zona arcuata, zona tecta.

Barnes zone: the lower fourth of the pregnant uterus, attachment of the placenta to any part of which may cause dangerous hemorrhage. SYN: cervical zone.

cervical zone: Barnes zone.

cervical zone of tooth: neck of tooth.

ciliary zone: the outer, wider zone of the anterior surface of the iris, separated from the pupillary zone by the collarette. SYN: zona ciliaris.

comfort zone: the temperature range between 28°C and 30°C at which the naked body is able to maintain the heat balance without either shivering or sweating; in the clothed body the range is from 13°C to 21°C.

zones of discontinuity: concentric zones of varying optical density in the lens of the eye, as seen in slitlamp biomicroscopy.

dolorogenic zone: trigger point.

entry zone: the area of the dorsal funiculus of the spinal cord, medial to the tip of the posterior horn, in which the entering fibers of the posterior nerve root divide into ascending and descending branches.

ependymal zone: ependymal layer.

epileptogenic zone: a cortical region that on stimulation reproduces the patient's spontaneous seizure or aura.

equivalence zone: in a precipitin reaction, the zone in which neither antibody nor antigen is in excess. SEE ALSO: precipitation. SYN: equivalence point.

erogenous zone, erotogenic zone: areas of the body, such as genitals and nipples, which elicit sexual arousal when stimulated.

fetal zone: fetal adrenal cortex.

gingival zone: that portion of the oral mucosa which surrounds the teeth and is firmly attached to the underlying alveolar bone.

Golgi zone: part of the cytoplasm occupied by the Golgi apparatus; in secretory cells of exocrine glands, a zone between the nucleus and the luminal surface.

grenz zone: in histopathology, a narrow layer beneath the epidermis that is not infiltrated or involved in the same way as are the lower layers of the dermis. [Ger. Grenze, borderline, boundary]

Head zones: Head lines, under line.

hemorrhoidal zone: the part of the anal canal that contains the rectal venous plexus. SYN: anulus hemorrhoidalis, zona hemorrhoidalis.

zones of hypothalamus: rostrocaudally oriented regions of the hypothalamus characterized by their position and cell groups. The periventricular zone (zona periventricularis) is a thin sheet of small neurons located in the wall of the third ventricle. The medial zone (zona medialis) lies between the periventricular zone and a rostrocaudal line drawn between the mammillothalamic tract and the postcommissural fornix, and consists of supraoptic, tuberal, and mammillary regions. The lateral zone (zona lateralis) is lateral to the medial zones, and contains the tuberal nuclei and the fibers of the medial forebrain bundle. SYN: zonae hypothalamicae .

intermediate zone of iliac crest: the line on the crest of the ilium between the outer and inner lips, for origin of internal oblique muscle. SYN: linea intermedia cristae iliacae , intermediate line of iliac crest.

interpalpebral zone: the exposed area of the cornea and sclera between the lids of the open eye.

intertubular zone: the dentinal matrix that lies between zones of peritubular dentin; it is less calcified and contains larger collagen fibers than does peritubular dentin.

Marchant zone: the area on the sphenoid and occipital bones at the base of the skull from which the dura mater is readily detached.

marginal zone:

A zone between the red and white pulp of the spleen containing numerous macrophages and a rich plexus of sinusoids supplied by white pulp arterioles carrying blood-borne antigens.

marginal layer.

medial zone: See zones of hypothalamus. SYN: zona medialis .

motor zone: that portion of the cerebral cortex, primarily the posterior region of the frontal lobe, near the central sulcus, which when stimulated produces a movement and when injured produces spasticity or paralysis.

neutral zone: in dentistry, the potential space between the lips and cheeks on one side and the tongue on the other; natural or artificial teeth in this zone are subject to equal and opposite forces from the surrounding musculature.

nucleolar zone: nucleolar organizer.

Obersteiner-Redlich zone: the narrow line along the course of a nerve (or nerve root) where the Schwann cells and connective tissue that support its axons are replaced by glia cells. The zone marks the true boundary between the central and the peripheral nervous system. Usually located at or near the surface of the spinal cord or brainstem, it can extend ( e.g., in the eighth nerve) several millimeters out along the nerve. SYN: Obersteiner-Redlich line.

polar zone: the region in the vicinity of an electrode applied to the body. SEE ALSO: electrotonus.

protective zone: the time in the cardiac cycle, immediately following the vulnerable period, during which a second stimulus will prevent the initiation of ventricular fibrillation by a previous stimulus applied during the vulnerable period, probably by blocking a reentrant pathway.

pupillary zone: the central region of the anterior surface of the iris located between the collarette and the pupillary margin. SYN: zona pupillaris.

reflexogenic zone: the area or zone where stimulation will elicit a given reflex.

secondary X zone: an adrenocortical zone, situated in the inner zona fasciculata, that appears upon postpubertal gonadectomy in some male rodents, most notably the mouse; the development of this zone is believed to be stimulated by pituitary gonadotropins.

segmental zone: in a young embryo, the thickened dorsal portion of the undifferentiated paraxial mesoderm that becomes metamerically divided to form the mesodermal somites. SYN: segmental plate.

Spitzka marginal zone: dorsolateral fasciculus.

subplasmalemmal dense zone: corneocyte envelope.

sudanophobic zone: a zone of cells, at the periphery of the zona fasciculata in the adrenal cortex of the rat, that is not stained by Sudan dyes.

tender zones: Head lines, under line.

thymus-dependent zone: paracortex.

trabecular zone: trabecular tissue of sclera.

transformation zone: zone on the cervix at which squamous epithelium and columnar epithelium meet; changes location in response to a woman's hormonal status.

transitional zone:

1. the equatorial region of the lens of the eye where the anterior epithelial cells become transformed into lens fibers

2. that portion of a scleral contact lens between the corneal and scleral sections.

transitional zone of lips: hairless thin skin beginning at the vermillion border of the lips; appears red because of underlying capillary bed.

trigger zone: trigger point.

trophotropic zone of Hess: an area in the hypothalamus concerned with rewarding bodily sensations.

vascular zone: an area in the external acoustic meatus where a number of minute blood vessels enter from the mastoid bone. SYN: spongy spot, zona vasculosa.

vermilion zone, vermilion transitional zone: vermilion border.

Weil basal zone: Weil basal layer.

Wernicke zone: Wernicke center.

zone 1, 2, 3, 4 of West: in pulmonary physiology, defines the levels in a vertical lung according to the relationships of alveolar gas pressure, capillary blood pressure, and pulmonary venous pressure.

X zone:

a transient adrenocortical zone present in some rodents at birth, most notably in mice, situated between the zona reticularis and the adrenal medulla; it degenerates in males with the secretion at puberty and in females during their first pregnancy; it slowly enlarges in unmated females after puberty and does not degenerate until middle age; the X zone appears to secrete no hormone; SYN: androgenic zone.

zoning (zon′ing)
The occurrence of a stronger reaction in a lesser amount of suspected serum, observed sometimes in serologic tests used in the diagnosis of syphilis, and probably the result of high antibody titer.

zonography (zo-nog′ra-fe)
A form of tomography with a relatively thick plane of focus; especially used in renal radiography. [zone + G. grapho, to write]

zonule (zo′nul, zon′ul)
A small zone. SYN: zonula.
ciliary z. a series of delicate meridional fibers arising from the inner surface of the orbiculus ciliaris that run in bundles between, and in a very thin layer over, the ciliary processes; at the inner border of the corona, the fibers diverge into two groups that are attached to the capsule on the anterior and posterior surfaces of the lens close to the equator; the spaces between these two layers of fibers are filled with aqueous humor. SYN: zonula ciliaris, apparatus suspensorius lentis, suspensory ligament of lens, Zinn z..
Zinn z. SYN: ciliary z..

zonulitis (zo-nu-li′tis)
Assumed inflammation of the zonule of Zinn, or suspensory ligament of the lens of the eye. [zonule + G. -itis, inflammation]

zoogeography (zo′o-je-og′ra-fe)
The geography of animals; the study of the distribution of animals on the earth's surface.

zooglea (zo-og′le-a, zo′o-gle′a)
In bacteriology, an old term for a mass of bacteria held together by a clear gelatinous substance. [zoo- + G. glia, glue]

zoogonous (zo-oj′o-nus)
SYN: viviparous.

zoogony (zo-oj′o-ne)
SYN: viviparity.

zoograft (zo′o-graft)
A graft of tissue from an animal to a human. SYN: animal graft, zooplastic graft.

zoografting (zo-o-graft′ing)
SYN: zooplasty.

zooid (zo′oyd)
1. Resembling an animal; an organism or object with an animal-like appearance. 2. An animal cell capable of independent existence or movement, as the ovum or a spermatozoon, or the segment of a tapeworm. 3. An individual of a colonial invertebrate, such as a coral. [G. zoodes, fr. zoon, animal, + eidos, resemblance]

zoom (zoom)
The action of a varifocal lens system in a camera or microscope that maintains an object in focus while approaching it or receding from it; this effect may be obtained by moving two or more of the lens components at rates bearing a linear relation to one another.

Zoomastigophorea (zo′o-mas-ti-go-fo′re-a)
A class of flagellates (superclass Mastigophora) within the phylum Sarcomastigophora (flagellate and ameboid protozoans), of animal-like as opposed to plantlike characteristics. Chromatophores are absent; one to many flagella are found, although they may be absent in ameboid forms; sexuality is known in some groups. It includes many human parasites such as the trypanosomes and trichomonads, as well as a number of other parasitic and symbiotic forms. SYN: Zoomastigina, Zoomastigophorasida. [zoo- + G. mastix, whip, + phoros, bearing]

direct zoonosis: a zoonosis transmitted between humans and other animals from an infected to a susceptible host by contact, by airborne droplets or droplet nuclei, or by some vehicle of transmission; the agent requires a single vertebrate host for completion of its life cycle and does not develop or show significant change during transmission; may include anthropozoonoses (rabies), zooanthroponoses (amebiasis), and amphixenoses (certain streptococcoses).

zoonotic (zo′o-not′ik)
Relating to a zoonosis.

zooparasite (zo-o-par′a-sit)
An animal parasite; an animal existing as a parasite.

zoopathology (zo-o-pa-thol′o-je)
The study or science of diseases of the lower animals.

zootoxin (zo-otok′sin)
A substance, resembling the bacterial toxins in its antigenic properties, found in the fluids of certain animals; e.g., in snake venom, the secretions of poisonous insects, eel blood. SYN: animal toxin.

zootrophic (zo-o-trof′ik)
Relating to or serving for the nutrition of the lower animals. [zoo- + Gr. trophe, nourishment]

zorubicin (zo-roo-bi-sin)
Semisynthetic derivative of daunorubicin; also similar to doxorubicin. Like those agents, z. exerts significant myocardial toxicity. Used as an antineoplastic in breast cancer.